Urea heating system and heating method thereof

ABSTRACT

A urea solution heating device prevents freezing of a urea solution by using exhaust gas of an engine. More particularly, a urea solution heating device may use a pressure difference between an exhaust gas pipe and a muffler to bypass the exhaust gas to exchange heat between the exhaust gas and the urea solution. The urea solution heating device may include an exhaust gas pipe, a muffler, a first bypass pipe diverged from the exhaust gas pipe, a urea solution tank to which the bypassed exhaust gas is supplied, a second bypass pipe connected to the muffler, and a heat exchanger, wherein the exhaust gas sequentially flows through the first bypass line, the heat exchanger, and the second bypass line by a pressure difference between the exhaust gas pipe and the muffler. An urea solution heating method is also described.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0097125 filed Sep. 26, 2011, the entire contents of which application is incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a urea solution heating device. More particularly, the present invention relates to a urea solution heating device that prevents freezing of a urea solution by using exhaust gas of an engine, and a method thereof.

2. Description of Related Art

Generally, a post-treatment art for exhaust gas is applied to reduce NOx emissions of a diesel engine. Recently, a new type of post-treatment art has been introduced to satisfy exhaust gas regulations such as EURO4 and EURO5. The post-treatment art is a method for reducing harmful material of exhaust gas that domestic and foreign countries closely pay attention to, and representative thereof are an EGR system and a urea-SCR system. Particularly, the urea-SCR system is an art that has been most widely used among the introduced post-treatment arts, in which a urea solution is injected to reduce NOx of exhaust gas, and fuel consumption efficiency, activation temperature, and purification rate thereof are relatively excellent.

More specifically, the urea-SCR (selective catalytic reduction) system reduces NOx of exhaust gas pollutants (HC, CO, PM, and NOx) of a diesel engine, wherein a urea solution is injected into the exhaust gas and the injected urea solution is transformed into NH3 and HNCO by the heat of the exhaust gas. Further, the HNCO is resolved by water of the exhaust gas to NH3 and CO2, and the NH3 reacts with NOx through a catalyst to become N2 and H2O.

However, the urea solution is frozen at lower than minus 11 degrees Celsius, and the frozen urea solution can cause a fatal defect in the urea-SCR system. Accordingly, two types of method for melting the urea solution have been introduced.

One of the methods is a heating method for heating the urea solution through a coil. This method measures the temperature of the urea solution of the urea tank through a temperature sensor, and the ECU supplies power through a relay such that the heat of the coil heats the urea solution. However, there is a problem that the coil needs to be disposed and there is a problem that the power is supplied through a relay in this method.

The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF INVENTION

Various aspects of the present invention provide for a urea solution heating device and a control method thereof having advantages of heating a urea solution by exhaust gas that is exhausted from an engine.

Various aspects of the present invention provide for urea solution heating device that may include an exhaust gas pipe through which exhaust gas of an engine is exhausted, a muffler that is connected to one end of the exhaust gas pipe to exhaust the exhaust gas outside, a first bypass pipe that is diverged from the exhaust gas pipe to bypass the exhaust gas, a urea solution tank to which the bypassed exhaust gas is supplied and in which a urea solution is filled, a second bypass pipe that is connected to the muffler and that supplies the exhaust gas passing the urea solution tank to the muffler, and a heat exchanger that is disposed in the urea solution tank to connect the first bypass pipe with the second bypass and through which the exhaust gas flows such that the exhaust gas heats the urea solution, wherein the exhaust gas sequentially flows through the first bypass line, the heat exchanger, and the second bypass line by a pressure difference between the exhaust gas pipe and the muffler.

A solenoid valve may be disposed on the first bypass pipe to selectively bypass the exhaust gas.

A temperature sensor may bedisposed on the urea solution tank to detect the temperature of the urea solution.

The urea solution heating device may further include a dosing control unit (DCU) that is connected to the solenoid valve and the temperature sensor, and receives a temperature signal of the urea solution from the temperature sensor to operate the solenoid valve.

An insulating member may bedisposed in the urea solution tank, both ends of the insulating member are opened and urea solution housing holes are formed in a side surface thereof, and one of the ends may beengaged with a urea solution tank cap to be closed.

The heat exchanger may bedisposed inside the insulating member.

The heat exchanger may bemade by bending a pipe having a predetermine length several times such that the urea solution exchanges heat with the exhaust gas flowing in the heat exchanger.

The heat exchanger may include two ends, and an exhaust gas suction hole is formed in one end and an exhaust gas outlet is formed in the other end.

The exhaust gas suction hole may beconnected to the first bypass pipe through the urea solution tank cap, and the exhaust gas outlet is connected to the second bypass line through the urea solution tank cap.

A urea solution outlet may beformed on the urea solution tank cap such that the urea solution of the urea solution tank is exhausted outside.

A urea solution pump may bedisposed at a surface of an interior direction of the insulating member of the urea solution tank cap to exhaust the urea solution in the urea solution tank to the outside through the urea solution outlet.

A sealing member may bedisposed between an interior circumference of the urea solution tank cap and an exterior circumference of the insulating member to prevent leakage of the urea solution.

A pressure sensor may bedisposed at one end of the first bypass pipe diverged from the exhaust gas pipe and at one end of the second bypass pipe connected to the muffler to detect exhaust gas pressure of the exhaust gas pipe and the muffler.

The DCU may beconnected to the pressure sensors to open the solenoid valve when the pressure difference between the exhaust gas pipe and the muffler is larger than a predetermined value.

Other aspects of the present invention provide for an urea solution heating method, in a urea solution heating device that includes an exhaust gas pipe exhausting exhaust gas of an engine, a muffler that is connected to the exhaust gas pipe, a urea solution tank in which a urea solution is filled, a bypass pipe that is diverged from the exhaust gas pipe to be connected to the muffler through the urea solution tank, and a solenoid valve that selectively open/closes the bypass pipe, may include the steps of determining whether a rotation speed of the engine is faster than an idle rotation speed of the engine (S100), determining whether a urea solution temperature is less than a predetermined value through a temperature sensor disposed in the urea solution tank (S110), determining whether a rotation speed of the engine is slower than a maximum rotation speed of the engine (S120), determining whether a load of the engine is less than a permissible value (S130), opening the solenoid valve if the steps S100, S110, S120, and S130 are satisfied (S150), closing the solenoid valve if one of the steps S100, S110, S120, and S130 is not satisfied (S160), and performing the procedures from step S100 again if step S150 or step S160 is performed.

As described, the urea solution may be heated by high temperature and pressure exhaust gas exhausted from the engine, and separate constituent elements such as a heating device or a power supply device are not necessary according to various aspects of the present invention.

Also, flow of exhaust gas may be controlled by a pressure difference between an exhaust pipe and a muffler, and therefore separate constituent elements for supplying exhaust gas to a urea solution tank are not necessary.

Accordingly, the device for heating the urea solution and the method are simplified and production cost can be saved.

The methods and apparatuses of the present invention have o her features and other advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary urea solution heating device according to the present invention.

FIG. 2 is an enlarged view showing an “A” part of FIG. 1.

FIG. 3 is a schematic diagram of an exemplary urea solution heating device according to the present invention.

FIG. 4 is a perspective view of an exemplary heat exchanger according to the present invention.

FIG. 5 is a flowchart for an exemplary urea solution heating method according to the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

FIG. 1 is a schematic diagram of a urea solution heating device according to various embodiments of the present invention.

As shown in FIG. 1, a urea solution heating device according to various embodiments of the present invention includes an exhaust gas pipe 10, a muffler 20, a urea solution tank 50, a heat exchanger 60, first and second bypass pipes 80 and 82, a solenoid valve 30, a temperature sensor 70, and a DCU 40.

The exhaust gas pipe 10 is connected to a combustion chamber of an engine to exhaust high temperature and high pressure exhaust gas of the engine.

The muffler 20 is a device that reduces pressure and temperature of exhaust gas to exhaust the exhaust gas to the outside. Also, the muffler 20 is connected to one end of the exhaust gas pipe 10. That is, one end of the exhaust gas pipe 10 is connected to the muffler 20, and the other end thereof is connected to the engine to supply the muffler 20 with the exhaust gas that is exhausted from the combustion chamber of the engine.

The urea solution tank 50 holds a urea solution that is used to treat the exhaust gas. Also, the urea solution tank 50 is separately disposed from the exhaust gas pipe 10 and the muffler 20.

The heat exchanger 60 is disposed in the urea solution tank 50 such that heat is exchanged between the exhaust gas and the urea solution.

The first and second bypass pipes 80 and 82 bypass a part of exhaust gas flowing in the exhaust gas pipe 10 such that the exhaust gas flows through the urea solution tank 50 to be transferred to the muffler 20. The first bypass pipe 80 is diverged from one side of the exhaust pipe 10 to be connected to the heat exchanger 60 that is disposed in the urea solution tank 50. Also, one end of the second bypass pipe 82 is connected to the heat exchanger 60 and the other end thereof is connected to the muffler 20. That is, a part of the exhaust gas flowing in the exhaust gas pipe 10 passes the first bypass pipe 80 to be supplied to the heat exchanger 60, heat is exchanged between urea solution and the exhaust gas in the heat exchanger 60, and the heat-exchanged exhaust gas is transferred to the muffler 20 through the second bypass pipe 82.

The solenoid valve 30 is used to selectively open the first bypass pipe 80. Also, the solenoid valve 30 is disposed on the first bypass pipe 80 between the exhaust gas pipe 10 and the urea solution tank 50.

The temperature sensor 70 measures the temperature of the urea solution that is filled in the urea solution tank 50. Also, the temperature sensor 70 can be disposed inside the heat exchanger that is disposed in the urea solution tank 50. Meanwhile, the position of the temperature sensor 70 in the urea solution tank 50 can be varied by a person of ordinary skill in the art.

The DCU 40 is a dosing control unit. The DCU 40 is separately disposed outside the urea solution tank 50 to be electrically connected to the temperature sensor 70 and the solenoid valve 30. Further, the DCU 40 receives the temperature signal of the urea solution filled in the urea solution tank 50 from the temperature sensor 70 and selectively opens or closes the solenoid valve 30. That is, if the temperature of the urea solution becomes less than a predetermined value, the solenoid valve 30 is opened so that the high temperature and high pressure exhaust gas is supplied to the urea solution tank 50. Meanwhile, the predetermined temperature can be varied by a person of ordinary skill in the art.

FIG. 2 is an enlarged view showing an “A” part of FIG. 1. That is, FIG. 2 is an enlarged view of a part where the first bypass pipe 80 is diverged from the exhaust gas pipe 10.

As shown in FIG. 2, the urea solution heating device according to various embodiments of the present invention further includes a nipple 12, a nipple penetration hole 14, a nipple cap 16, a nipple cap penetration hole 18, and a wrinkle pipe 84 around a part where the first bypass pipe 80 is diverged from the exhaust gas pipe 10.

The nipple 12 is integrally formed with a side surface of the exhaust gas pipe 10 such that the exhaust gas pipe 10 is engaged with the first bypass pipe 80. Also, the nipple 12 protrudes on a side surface of the exhaust gas pipe 10.

The nipple penetration hole 14 is formed such that a part of the exhaust gas flowing in the exhaust gas pipe 10 is supplied to the first bypass pipe 80. That is, the nipple penetration hole 14 is formed to penetrate the side surface of the nipple 12 and the exhaust gas pipe 10.

The nipple cap 16 is disposed at one end of the first bypass pipe 80 such that the exhaust gas pipe 10 is engaged with the first bypass pipe 80. Also, the nipple cap 16 covers the outside of the nipple 12 that is protruded to be engaged therewith. Further, a screw thread is formed on an outside surface of the nipple 12 and on an inside surface of the nipple cap 16. The nipple cap 16 can be integrally formed with one end of the first bypass pipe 80 or can be engaged with one end thereof.

The nipple cap 16 penetrates the exhaust gas pipe 10 in a vertical direction thereof such that the nipple cap penetration hole 18 forms one penetration passage together with the nipple penetration hole 14. As described above, one end of the first bypass pipe 80 is integrally formed with the nipple cap penetration hole 18 or is engaged therewith to be able to form one passage.

A method that is equal to the engagement method of the nipple 12 and the nipple cap 16 can be applied in an engagement structure of the muffler 20 and the second bypass pipe 82. The passage in the nipple penetration hole 14 and the nipple cap penetration hole 18 can be formed to be the same. A combination using the nipple 12 and the nipple cap 16 is shown in FIG. 2, but the combination can be varied by a person of ordinary skill in the art.

The wrinkle pipe 84 can be formed in a part of the first bypass pipe 80 so as to reduce an impact that can be generated in the first bypass pipe 80. The wrinkle pipe 84 is prepared as a damping device in FIG. 2, but various methods can be applied thereto by a person of ordinary skill in the art so as to reduce the impact or vibration.

FIG. 3 is a schematic diagram of a urea solution heating device according to various embodiments of the present invention.

Detailed description for constituent elements that are equat to that of the FIG. 1 will be omitted in FIG. 3.

As shown in FIG. 3, the urea solution heating device according various embodiments of the present invention further includes first and second pressure sensors 90 and 92.

The first pressure sensor 90 is disposed on the first bypass pipe 80. Also, the first pressure sensor 90 can be disposed at a part where the first bypass pipe 80 is diverged from the exhaust gas pipe 10 so as to measure the pressure of the inside of the exhaust gas pipe 10.

The second pressure sensor 92 is disposed on the second bypass pipe 82. Also, the second pressure sensor 92 can be disposed at a part where the second bypass pipe 80 is engaged with the muffler 20 so as to measure the pressure of the inside of the muffler 20.

The first and second pressure sensors 90 and 92 are connected to the DCU 40. The DCU 40 receives the pressure signal of the inside of the exhaust gas pipe 10 and the muffler 20 from the first and second pressure sensors 90 and 92 to selectively open or close the solenoid valve 30. That is, if the pressure difference between the exhaust gas pipe 10 and the muffler 20 becomes larger than a predetermined value, the solenoid valve 30 is opened so that the high temperature and high pressure exhaust gas is supplied to the urea solution tank 50. The predetermined value of the pressure difference can be varied by a person of ordinary skill in the art.

Accordingly, various embodiments of the present invention, such as that shown in FIG. 3 gathers data on the urea solution temperature and exhaust gas pressure and opens the solenoid valve 30 if the predetermined temperature or the predetermined pressure is satisfied. Also, a condition in which the pressure of the exhaust gas pipe 10 is higher than that of the muffler 20 is used in various embodiments shown in FIG. 1 and FIG. 3. That is, when the solenoid valve 30 is opened, a part of the exhaust gas flowing in the exhaust gas pipe 10 is naturally supplied to the muffler 20 through the first bypass pipe 80, the heat exchanger 60, and the second bypass pipe 82.

FIG. 4 is a perspective view of a heat exchanger according to various embodiments of the present invention.

As shown in FIG. 4, the heat exchanger 60 includes an insulating member 62, a urea solution tank cap 102, a heat exchange pipe 110, an exhaust gas suction hole 112, an exhaust gas outlet 114, a urea solution outlet 104, and a urea solution pump 100.

The insulating member 62 prevents the heat from being wasted to improve heat exchange efficiency between the exhaust gas and the urea solution. The insulating member 62 has a pipe shape of which both ends are opened. A plurality of urea solution housing holes 64 are formed to penetrate the insulating member 62such that the urea solution is supplied to the heat exchanger 60.

The urea solution tank cap 102 can be a cover of the urea solution tank 50. The urea solution tank cap 102 covers one of the opened ends of the insulating member 62 to be engaged with the insulating member 62. That is, one of the opened both ends of the insulating member 62 is closed by the urea solution tank cap 102. The insulating member 62 has a cylindrical shape of which both ends thereof are opened, and the urea solution tank cap 102 has a cylindrical shape of which one of the ends is closed. A sealing member 106 is disposed between an interior circumference of the urea solution tank cap 102 and an exterior circumference of the insulating member 62.

The heat exchange pipe 110 is disposed in an interior space of the insulating member 62 that is encircled by the insulating member 62 and the urea solution tank cap 102. The heat exchange pipe 110 has a predetermined length such that the heat exchange is sufficiently performed between the urea solution and the exhaust gas. The heat exchange pipe 110 having the predetermined length is formed by being bent several times such that it may be disposed in a limited space of the insulating member 62.

The heat exchange pipe 110 has two ends. One end is connected to the first bypass pipe 80 and the other end is connected to the second bypass pipe 82 such that the first bypass pipe 80, the heat exchange pipe 110, and the second bypass pipe 82 form one passage line.

The exhaust gas suction hole 112 is integrally formed with one end of the heat exchange pipe 110. One will apprecaite that the exhaust gas suction hole and the heat exchange pipe may be monolithically formed. One end penetrates the urea solution tank cap 102 to be protruded outside the urea solution tank 50. The exhaust gas suction hole 112 that protrudes outside the urea solution tank 50 is connected to the first bypass pipe 80.

The exhaust gas outlet 114 is integrally formed with the other end of the heat exchange pipe 110. One will apprecaite that the exhaust gas outlet and the heat exchange pipe may be monolithically formed. The other end penetrates the urea solution tank cap 102 to be protruded outside the urea solution tank 50. The exhaust gas outlet 114 that protrudes outside the urea solution tank 50 is connected to the second bypass pipe 82. That is, a part of the exhaust gas flowing in the exhaust gas pipe 10 is sequentially supplied to the muffler through the first bypass pipe 80, the heat exchange pipe 110, and the second bypass pipe 82.

The urea solution outlet 104 protrudes on an exterior surface of the urea solution tank cap 102 to exhaust the urea solution of the urea solution tank 50 to the outside. The exhausted urea solution can be used to treat the exhaust gas. The usage of the urea solution for treating the exhaust gas can be performed by a person of ordinary skill in the art, and therefore a detailed description thereof will be omitted.

The urea solution pump 100 pumps the urea solution to the outside of the urea solution tank 50. The urea solution pump 100 is disposed on an interior surface of the urea solution tank cap 102 to exhaust the urea solution through the urea solution outlet 104.

Hereinafter, a urea solution heating method will be described according to various embodiments of the present invention with reference to FIG. 5.

FIG. 5 is a flowchart for a urea solution heating method according to various embodiments of the present invention.

As shown in FIG. 5, the engine is started in S100, and the DCU 40 determines whether a rotation speed of the engine is faster than an idle rotation speed of the engine in S110.

If the rotation speed of the engine is faster than the idle rotation speed in S110, the DCU 40 receives the temperature data of the urea solution from the temperature sensor 70 that is disposed in the urea solution tank 50 to determine whether the urea solution temperature is less than a predetermined value in S120.

If the rotation speed of the engine is slower than the idle rotation speed in S110, the DCU 40 closes the solenoid valve 30 in S160.

If the urea solution temperature is lower than a predetermined temperature in S120, the DCU 40 determines whether the rotation speed of the engine is slower than a maximum rotation speed in S130.

If the urea solution temperature is higher than a predetermined value in S120, the DCU 40 closes the solenoid valve 30 in S160.

If it is determined that the present rotation speed of the engine is less than the maximum rotation speed in S130, the DCU 40 determines that the load of the engine is less than a permissible value in S140.

If it is determined that the present rotation speed of the engine is greater than the maximum rotation speed in S130, the DCU 40 closes the solenoid valve 30 in S160.

If it is determined that the load of the engine is less than a permissible value in S140, the DCU 40 opens the solenoid valve 30 in S150. That is, the solenoid valve 30 is opened in S150 if S100, S110, S120, and S130 are all satisfied.

If it is determined that the load of the engine is larger than the permissible value in S140, the DCU 40 closes the solenoid valve 30 in S160. That is, the solenoid valve 30 is closed in S160 if one of S100, S110, S120, and S130 is not satisfied.

If S150 or S160 is performed, S100 is performed again by the DCU 40 and sensors.

Data for the engine is detected by the ECU, the DCU 40 receives the data for the engine from the ECU, and S110, S130, and S140 can be performed thereby.

For convenience in explanation and accurate definition in the appended claims, the terms inside or outside, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A urea solution heating device, comprising: an exhaust gas pipe through which exhaust gas of an engine is exhausted; a muffler connected to one end of the exhaust gas pipe to exhaust the exhaust gas outside; a first bypass pipe diverging from the exhaust gas pipe to bypass the exhaust gas; a urea solution tank filled with urea solution to which the bypassed exhaust gas is supplied; a second bypass pipe connected to the muffler and that supplies the exhaust gas passing the urea solution tank to the muffler; and a heat exchanger disposed in the urea solution tank to connect the first bypass pipe with the second bypass and through which the exhaust gas flows such that the exhaust gas heats the urea solution, wherein the exhaust gas sequentially flows through the first bypass line, the heat exchanger, and the second bypass line by a pressure difference between the exhaust gas pipe and the muffler.
 2. The urea solution heating device of claim 1, wherein a solenoid valve is disposed on the first bypass pipe to selectively bypass the exhaust gas.
 3. The urea solution heating device of claim 2, wherein a temperature sensor is disposed on the urea solution tank to detect the temperature of the urea solution.
 4. The urea solution heating device of claim 3, further comprising a dosing control unit (DCU) connected to the solenoid valve and the temperature sensor, and receives a temperature signal of the urea solution from the temperature sensor to operate the solenoid valve.
 5. The urea solution heating device of claim 1, wherein an insulating member is disposed in the urea solution tank, both ends of the insulating member are opened and urea solution housing holes are formed in a side surface thereof, and one of the ends is engaged with a urea solution tank cap to be closed.
 6. The urea solution heating device of claim 5, wherein the heat exchanger is disposed inside the insulating member.
 7. The urea solution heating device of claim 6, wherein the heat exchanger is made by bending a pipe having a predetermine length several times such that the urea solution exchanges heat with the exhaust gas flowing in the heat exchanger.
 8. The urea solution heating device of claim 6, wherein the heat exchanger includes two ends, and an exhaust gas suction hole is formed in one end and an exhaust gas outlet is formed in the other end.
 9. The urea solution heating device of claim 8, wherein the exhaust gas suction hole is connected to the first bypass pipe through the urea solution tank cap, and the exhaust gas outlet is connected to the second bypass line through the urea solution tank cap.
 10. The urea solution heating device of claim 5, wherein a urea solution outlet is formed on the urea solution tank cap such that the urea solution of the urea solution tank is exhausted outside.
 11. The urea solution heating device of claim 10, wherein a urea solution pump is disposed at a surface of an interior direction of the insulating member of the area solution tank cap to exhaust the urea solution in the urea solution tank to the outside through the urea solution outlet.
 12. The urea solution heating device of claim 5, wherein a sealing member is disposed between an interior circumference of the urea solution tank cap and an exterior circumference of the insulating member to prevent leakage of the urea solution.
 13. The urea solution heating device of claim 4, wherein a pressure sensor is disposed at one end of the first bypass pipe diverged from the exhaust gas pipe and at one end of the second bypass pipe connected to the muffler to detect exhaust gas pressure of the exhaust gas pipe and the muffler.
 14. The urea solution heating device of claim 13, wherein the DCU is connected to the pressure sensors to open the solenoid valve when the pressure difference between the exhaust gas pipe and the muffler is larger than a predetermined value.
 15. A urea solution heating method, in a urea solution heating device that includes an exhaust gas pipe exhausting exhaust gas of an engine, a muffler connected to the exhaust gas pipe, a urea solution tank filled with a urea solution, a bypass pipe diverging from the exhaust gas pipe to be connected to the muffler through the urea solution tank, and a solenoid valve that selectively open/closes the bypass pipe, comprising the steps of: determining whether a rotation speed of the engine is faster than an idle rotation speed of the engine (S100); determining whether a urea solution temperature is less than a predetermined value through a temperature sensor disposed in the urea solution tank (S110); determining whether a rotation speed of the engine is slower than a maximum rotation speed of the engine (S120); determining whether a load of the engine is less than a permissible value (S130); opening the solenoid valve if steps S100, S110, S120, and S130 are satisfied (S150); closing the solenoid valve if one of steps S100, S110, S120, and S130 is not satisfied (S160); and performing the procedures from step S100 again if step S150 or step S160 is performed. 